As mobile phones and personal information terminals are rapidly becoming popular, there is an increasing demand for such devices that are more compact, lightweight and, at the same time, functionally sophisticated. Compact, lightweight and functionally sophisticated devices of the type under consideration entail development of high speed operating circuit boards and an enhanced level of integration, which by turn give rise to various problems including signal delays and EMIs (electromagnetic interferences). Expectations are high with regard to optical wiring techniques that can overcome or reduce the problems of signal delays, signal degradations and electromagnetic interferences produced from wires as such problems are serous with conventional electric wiring. Known devices that exploit advantages of optical wiring include the following.
An optoelectronic circuit board as disclosed in U.S. Pat. No. 5,835,646 is so designed that an optical wiring section and an electric wiring section are separated from each other therein and light being propagated through an optical waveguide arranged on a base member is modulated by driving an optical switch or an optical modulator also arranged on the base member according to a voltage signal from an electronic device so as to convert an electric signal into an optical signal in order to transmit it and also convert an optical signal into an electric signal by means of a light receiving element arranged on said base member or some other base member in order to convey the signal to some other electronic device or to the same electronic device. An optical waveguide device as disclosed in Japanese Patent Application Laid-Open No. 2000-199827 is so designed that a mirror is formed in a linear polymer waveguide in order to efficiently couple beams of light going out from or entering the optical waveguide perpendicularly relative to the latter.
The technique as disclosed in U.S. Pat. No. 5,835,646 is intended to compensate the problems of electric wiring by optical wiring. However, because optical wiring provides a transmission line (linear polymer waveguide), the site for electric/optical signal conversion or optical/electric signal conversion can automatically be defined and hence is limited. On the other hand, with the technique as disclosed in Japanese Patent Application Laid-Open No. 2000-199827, it can be difficult to mount a light emitting element on a linear optical waveguide having at an end thereof a mirror that is inclined by 45° so as to efficiently couple optical signals and to mount a light receiving element on the linear optical waveguide so as to efficiently receive an optical signal propagated through the latter because such a technique requires a high alignment accuracy. Additionally, because the technique involves the use of a linear optical waveguide, the position of the light emitting element and that of the light receiving element can be restricted to reduce the design freedom particularly when a plurality of optical waveguides need to be formed.